Recycling of slag and lead-bearing sludge in the cleaner production of alkali activated cement with high performance and microbial resistivity

The motivation behind this work is to sustainable utilization of water-cooled steel-slag and lead-bearing sludge (LBS: from glass crystal industry) in the cleaner production of alkali activated cement (AAC) with high performance and microbial resistivity. To prepare AAC, slag was individually blended with different LBS contents (0, 10, 30, and 50% with respect to weight of slag), then activated with sodium hydroxide (NaOH). Due to high CO2 emission resulting from NaOH-manufacturing, alkali activator was used with low concentration (3 wt, %) for activating the aluminosilicate precursors. A preliminary investigation proved that the mechanical and physical properties of AAC significantly enhanced with the increase of LBS content up to 30 wt %; meanwhile, 50 wt % LBS had a negative effect. The leaching test indicated that Pb-concentrations (mg/l) in leachate of all AAC-mixtures were below the safe limit of toxicity characteristic leaching procedure (TCLP). Agar diffusion test showed that the anti-bacterial and -fungal activity of AAC enhanced with increasing LBS content up to 50 wt %. From the standpoint of environmental impact assessment, the prepared cement showed 50-times lower CO2 emission compared with Portland cement.